Electricity

Let’s Review… Atoms have 3 subatomic particles Protons = positive Electrons = negative Neutrons = neutral Neutral Atom “Normal” state # Protons = # Electrons Charged Atom (atom with a positive or negative charge) Object must gain or lose electrons ONLY THE ELECTRONS MOVE Measured in Coulombs

Charge & Force Attraction Repulsion Rules of Charge “Opposites Attract” Attraction Forces pull together Repulsion Forces push apart Rules of Charge Like charges repel (+/+ or -/-) Opposite charges attract (+/-) + - +

Electricity Definition: Electricity is the energy associated with charged particles as they move from place to place The type of material determines how charges move through them Conductors Materials that allow electric charges to move easily Metals Insulators Materials that do NOT allow electrons to flow freely Rubber, plastic

Forms of Electricity Static Current Due to build up of charges in or on an object Current The flow of electrons in a circuit

Static Electricity Static electricity is electricity “AT REST” Occurs between 2 objects that become oppositely charged Objects involved have unequal electric charges Examples Clothes sticking together in the dryer (if no dryer sheet is used) Hair standing up after being brushed (on days with low humidity)

Lightning Large discharge of static electricity (electrons transferred from a cloud to the Earth) Friction from movement of water drops in a cloud build up positive and negative charges Bolts can deliver 100 million volts Safest place to be in a lightning storm is inside Lightning rods are grounded to Earth to distribute the charge

Electric Circuit An electric circuit is a path for the electrons to flow Flowing Electrons = current Electricity can only flow through a CLOSED circuit (not an open one) Hi-Lite This!

Voltage (Potential Difference) The PUSH that makes electrons flow (electrons have potential to flow but won’t on their own) A difference between energy levels is needed for flow Electrons flow in a circuit when there is an energy difference from one end of the energy source to the other end of the energy source (like a battery) Units = VOLTS (V) Symbol = V (capital) Measured with a Voltmeter

Electric Current The FLOW of electric charges in a circuit Units = Amperes (amps) Symbol = I Speed of Current is affected by Type, length, & thickness of wire Voltage When Voltage , Current 

2 Types of Electric Current Direct Current (DC) Electron flow is always in the same direction Ex: Batteries Alternating Current (AC) Electrons reverse the direction of flow 60 times per second Ex: Electricity in the Home

Resistance Opposition to the flow of electrons Unit = Ohm (Ω) Symbol = R Highest resistance in: Poor conductors Thin wires Long wires

Relates Electric Current, Voltage, & Resistance Ohm’s Law Relates Electric Current, Voltage, & Resistance V = I x R Voltage (volts, V) Current (amps) Resistance (ohms, Ω)

V = I x R Ohm’s Law Example Calculate the voltage across a 3Ω resistor if a 0.5 amp current is flowing through it. V = I x R

V = I x R Ohm’s Law Example Calculate the voltage across a 3Ω resistor if a 0.5 amp current is flowing through it. V = I x R V = ? R = 3 Ω I = 0.5 amp

V = I x R Ohm’s Law Example Calculate the voltage across a 3Ω resistor if a 0.5 amp current is flowing through it. V = I x R V = ? R = 3 Ω I = 0.5 amp V = (0.5 amp)*(3 Ω )

V = I x R Ohm’s Law Example Calculate the voltage across a 3Ω resistor if a 0.5 amp current is flowing through it. V = I x R V = ? R = 3 Ω I = 0.5 amp V = (0.5 amp)*(3 Ω ) V = 1.5 v

V = I x R Ohm’s Law Example 2 A radio with a resistance of 240 Ω is plugged into a 120 v outlet. What is the current flowing through the outlet? V = I x R

V = I x R Ohm’s Law Example 2 A radio with a resistance of 240 Ω is plugged into a 120 v outlet. What is the current flowing through the outlet? V = I x R V = 120 v I = ? R = 240 Ω

V = I x R Ohm’s Law Example 2 A radio with a resistance of 240 Ω is plugged into a 120 v outlet. What is the current flowing through the outlet? V = I x R V = 120 v I = ? R = 240 Ω 120 v = I * 240 Ω

V = I x R Ohm’s Law Example 2 A radio with a resistance of 240 Ω is plugged into a 120 v outlet. What is the current flowing through the outlet? V = I x R V = 120 v I = ? R = 240 Ω 120 v = I * 240 Ω I = 120v / 240 Ω

V = I x R Ohm’s Law Example 2 A radio with a resistance of 240 Ω is plugged into a 120 v outlet. What is the current flowing through the outlet? V = I x R V = 120 v I = ? R = 240 Ω 120 v = I * 240 Ω I = 0.5 amp I = 120v / 240 Ω

P = I x V Power RATE at which energy is flowing The measure of the RATE at which electricity does work or provides energy Symbol = P Units = Watts (W) P = I x V

Power Example If a CD player uses 4.5v with 0.2 amp current, how much power does it use? P = I x V

P = I x V Power Example P= ? I = 0.2 amp V= 4.5 v If a CD player uses 4.5v with 0.2 amp current, how much power does it use? P = I x V P= ? I = 0.2 amp V= 4.5 v

P = I x V Power Example P= ? I = 0.2 amp V= 4.5 v P = I * V If a CD player uses 4.5v with 0.2 amp current, how much power does it use? P = I x V P= ? I = 0.2 amp V= 4.5 v P = I * V

P = I x V Power Example P= ? I = 0.2 amp V= 4.5 v P = I * V If a CD player uses 4.5v with 0.2 amp current, how much power does it use? P = I x V P= ? I = 0.2 amp V= 4.5 v P = I * V P = (0.2amp)(4.5v)

P = I x V Power Example P= ? I = 0.2 amp V= 4.5 v P = I * V If a CD player uses 4.5v with 0.2 amp current, how much power does it use? P = I x V P= ? I = 0.2 amp V= 4.5 v P = I * V P = (0.2amp)(4.5v) P = 0.9 W

E = P x t ELECTRICAL Energy Home use of electric energy is based on the AMOUNT OF ELECTRICAL POWER used per hour Measured in kilowatt hours (1000 Watts per hour) = kWh E = P x t

Electrical Energy Example You use your hairdryer for 20 minutes everyday. The hairdryer uses 1000 kW. How many kilowatt-hours does your hairdryer use in 6 days? t = 20min/day*6days = 120min = 2hr E = 1000 kW*2Hr E = 2000 kWh

Circuits Closed loop made up of at least two electrical elements Consists of at least a power source, wire, and a device that uses electrical energy (like a light bulb)

Symbols for Circuit Diagrams Positive Side of Power Source Wire Power Source Bulb Resistance Switch (open) (closed) Negative Side of Power Source

Open Circuit Light will not go on because the wire IS NOT CONNECTED to the battery on both sides; current will NOT flow

Closed Circuit Light bulb turns on because the electrical current CAN now flow through the complete circuit

Series Circuit All parts of the circuit are connected one after another in a loop There is only one path for the electrons to follow If one part goes out The circuit goes from closed to open Electricity will not flow All parts go out The voltage is split through each part of the circuit The current is the same throughout the circuit Example: Christmas Tree Lights

Series Circuit Examples A complete circuit turns the light bulbs on

Series Circuit Examples This Light Bulb is Burnt Out The burnt bulb stops the electron flow to the rest of the circuit

Parallel Circuit There is more than one path or branch for the electrons If a break occurs in one branch, the electrons can still flow in the other The voltage is the same throughout each branch The current is split through each branch Example: Household Wiring

Parallel Circuit Examples B A PATH #1 PATH #2 Current divides and has more than one path

Parallel Circuit Examples This Light Bulb is Burnt Out A B Even though Bulb “B” is burnt out, the current still goes through the other circuit and Bulb “A” remains lit